NATURAL SYSTEMS.— MACLEAY. 207 
sketch,” observes our author, “‘ we are at first struck 
with the analogy which opposite points of the same 
circle bear to one another,—an analogy sometimes so 
strong that it has been mistaken for a relation of affinity ; 
and, indeed, I am still unable to state whether this be 
not the fact, and that the opposite points of the curve, 
if I may so express myself, do not meet each other. 
Thus the resemblance which the intestinal Acrita (In- 
testina) or Monogena of Latreille bear to the Nematoidea 
of Rudolphi, and the Annelides, need not be descanted 
on, nor the affinity which the Cirripeda, according to 
some naturalists, appear to have with the branchiopod 
Mollusca. It will be sufficient to state, that as this 
peculiarity of natural distribution was detected by ana- 
lysis in the former part of this work, and the use to be 
made of it was visible among the Petalocera, so the dis- 
covery of it served to prevent my falling into several 
mistakes, which I could not otherwise have avoided, in 
deciding between relations of analogy and affinity, as 
they exist in the more general groups. The quadruped 
reptiles may, in this way, be separated from the Mam- 
malia by the intervention of birds on one hand, and of 
fishes on the other ; and yet Dumeril may, possibly, 
not be far wrong in urging that the paradoxical orni- , 
thorhynchus bears a nearer relation to reptiles than to_/ 
birds. But my province more particularly is entomo- 
logy ; and this property of a distribution, which, for 
convenience only, we have considered as circular, will 
serve to make the hexapod Acaride approach to the 
Anoplura of Leach, as appears to be the case in nature.” * 
That the meaning of this passage may be rendered more 
clear to the student, we must beg his attention to the 
following , diagram, — which, in its outlines, is pre- 
cisely the same as the former, but those groups, not 
now alluded to, are omitted, while those which are sup- 
posed to “‘ meet each other,” that is, to unite, are in- 
dicated by dotted lines. 
* Hor. Ent. p. 319. 
